Cathode ray apparatus



Nov. 30, 1937.

R. URTEL 2,160,618

CATHODE RAY APPARATUS Filed Dec. 14, 1954 2 Sheets-Sheet l INVENTOR ATTORN EY R. URTEL Nov. 30, 1937.

CATHODE RAY APPARATUS Filed Dec. 14, 1934 2 Sheets-Sheet 2 INVENTOR 191/000 (/8761 BY ATTORNEY Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE CATHODE RAY APPARATUS Germany Application December 14, 1934, Serial No. 757,436 In Germany December 7, 1933 4 Claims.

This invention relates particularly to means to insure coordinate deflection of the cathode ray beam developed within a cathode ray tube.

The invention is concerned with the magnetic deflection of cathode ray pencils in oscillograph and similar tubes, especially when the tubes are used for television work. The means for deflection of the ray is adapted to produce magnetic deflection for the shifting of the spot in the direction of the picture lines. For the optical transmitter an arrangement is presupposed which has constant scanning speed along picture lines, such as a perforated or Nipkow disk or a mirror wheel scanner, or where desired a cathode ray transmitter system such as Zworykin has described in many publications.

Illustrative of my invention are the drawings in which Fig, 1 is a graphical representation of a sawtooth current;

Fig. 2 is a graphical representation of a distorted saw-tooth current;

Fig. 3 shows one of the known forms of making deflecting coils;

Fig. 4 shows one embodiment of my invention for winding deflection coils;

Fig. 5 shows a modification of an embodiment of my invention; and

Fig. 6 shows another modification of my invention.

Synchronous line motion of the spot in the receiver apparatus which must be aimed at in the case of such an arrangement would be obtained if a strictly serrated current curve were producible in the deflecting coil. Fig. 1 shows the ideal form of the current in which the return interval t should be as brief as possible in contrast with the line duration T. During period T the rise of the current should occur linearly in order that the movement of the receiving spot may remain congruent relative to the sending spot both as regards time and space.

However, this ideal condition is not readily attainable in practice when recourse is had to magnetic deflection of the cathode ray pencil. On the contrary, due to the inductance of the deflector coil, there is brought about a distortion of the shape of the current curve of the kind approximately shown by way of example in Fig. 2. In the television picture, this manifests itself in a corresponding distortion of the grate inasmuch as the rise of the current inside portion a occurs more slowly than in part b so that a rise of current in direct proportion to the time is out of the question. What thus happens is an undesirable crowding together of the elementary picture points at the beginning of the line near a, i. e., towards one edge of the picture field. What is troublesome also is the relatively long return period of the spot (0 in Fig. 2).

The deformation of the grating may be diminished by reducing the coil inductance, for instance, by reducing the number of turns of the coil. If incidentally no loss of sensitiveness of the deflecting means is to happen, the coil must be placed at greater proximity to the cathode ray pencil. However, a final limitation is imposed upon such approach of the coil to the cathode ray pencil by the diameter of the neck of the tube unless, as has been suggested in the prior art, the coil is to be accommodated inside the tube. However, such a disposition would mean a loss of the chief advantages resulting from the use of magnetic deflecting coils, namely, substantially simpler manufacture of the tube, absence of any lead-ins or seals for the coordinate deflecting means and ease of adjustment of individual coils or coil systems at any desired time after completion of a tube.

In the present invention, arrangement of the coils outside the tube is preserved. However, by choosing a novel shape and disposition for the deflection coils compared with former arrangements as shown, for instance, in Fig. 3, considerable reduction of the inductance is to be obtained for the same sensitiveness. The guiding idea in the invention has been to so build the deflecting coils that maximum utilization of the magnetic field of the coil for coordinate deflection is attainab e.

One exemplified embodiment of the basic idea of the invention is shown in Fig. 4. S is a coil continuously wound or composed. of suitably assembled parts and tightly surrounding the neck of the tube in a way as shown for causing deflection in one coordinate direction. The turns of the coil, as shown, should preferably be given a form oblong in axial direction of the tube, say, rectangular form in order that the electrons of the cathode ray pencil may be acted upon over a longer distance of their travel and path. Deflection in the other coordinate sense is accomplishable by an ordinary pair of coils disposed at right angles to the direction of the field of the first coil and outside the latter. It is preferable in this connection to insure the coordinate deflection involving the greater period by the aid of the outer coils inasmuch as these, as a general rule, will involve the higher inductance.

Referring to Fig. 5, S2 and S3 represent the pair of coils, R is the neck of the tube which is directly surrounded by the coil SI. In order that the magnetic fiux outwardly may be minimized, and in order that the sensitivity for the same consumption of current may be maximized, the assembly is short-circuited magnetically by an iron yoke J.

In the embodiment shown in Fig. 5 it has been found that an undesirable field distortion is liable to happen owing to the circumstance that force-lines will extend not only parallel to the coils S2 and S3, but also towards the neighboring wide pole-shoes of coil SI. This shortcoming may be obviated by improving the arrangement shown in Fig. 4 in that over coil SI another similar coil is wrapped whose force lines will intersect with those of the coil SI at right angles. The principle underlying the winding in this case is schematically illustrated in Fig. 6. WI is the inner winding, for instance, for the production of the more speedy line deflection, W2 the winding disposed at right angles thereto and outside the former adapted for the slower picture deflection. Because of the low picture frequency the outer coil may here be given a greater number of coils. The efiectiveness of such a coil system may considerably increased also by the aid of an iron yoke. A disposition of this kind when compared with the deflector system shown in Fig. 3 secures a reduction of inductance to ca at the same sensitiveness and greatest freedom from distortion.

It will be noted that the form of the winding shown in Fig. 6 substantially eliminates any magnetic field set up by the coils parallel to the axis of the tube, because the field set up by one of the semi-circular portions of a turn is neutralized by the field set up by the other semi-circular portionof another turn lying in the same plane as the first turn. This is so since the current fiow in both of the semi-circular portions is in the same direction, but due to the opposite curvature of these portions, the fields set up perpendicular to the plane containing the two semicircular portions are of opposite sign and since a symmetrical array is provided, both of the fields are of equal magnitude. Having equal magnitude by opposite signs, they, therefore, neutralize each other. The direction of the magnetic fields produced can be verified by the well known right-hand rule which is well known in the art of magnetics.

Having thus described the invention, what is claimed is: V v

1. In combination, a cathode ray tube comprising an envelope, said envelope having a'cylindrical neck portion through which a developed electron beam passes, means for magnetically defiecting said electron beam, said means comprising a winding disposed upon said neck and adapted to produce the magnetic field at right angles to said electron beam, and said winding shaped so that every plane perpendicular to said produced magnetic field which passes through said cylindrical neck also passes through a portion of the winding serving to produce the magnetic field.

2. In combination, a cathode ray tube comprising an envelope, said envelope having a cylindrical neck portion through which a developed electron beam passes, means for magnetically deflecting said electron beam, said means comprising a winding disposed upon said neck and adapted to produce the magnetic field at 7 right angles to said electron beam, said winding tron beam passes, means for magnetically defiecting said electron beam, said deflecting means comprising a winding disposed about said neck so as to produce within the tube neck a magnetic field at right angles to said electron beam, said winding being so shaped that every plane perpendicular to said produced magnetic field which passes through said cylindrical neck also passes through a portion of the winding serving to pro duce the magnetic field, a second set of deflecting coils mounted at right angles to said first set of coils, and a magnetic core surrounding said deflecting coils to prevent leakage reaction between said coils.

4. In combination, a cathode ray tube comprising an envelope, said envelope having a cylindrical neck portion through which a developed electron beam passes, means for magnetically deflecting said electron beam, said means comprising a winding having one of its peripheries in a plane perpendicular to the axis of the tube and certain portions of the said Winding being in magnetic opposition to certain other portions of said Winding for neutralizing the magnetic fields set up in said portions during operation of said tube.

RUDOLF UR'IEL. 

